Flapper or reed valves are used in various types of applications where a specific type of compression cycle is regulated for a specific purpose. It can be a refrigeration cycle in a hermetic reciprocating compressor working uninterrupted in a refrigerator or in the air conditioner of a car. A flapper valve is basically a spring made from a pre-hardened steel strip. In its simplest form, the flapper valve is tongue shaped, where one end is fixed and the opposite end hangs free and regulates the liquid or gas flow in the compressor. The flapper valve suffers from both cyclic bending stresses and cyclic impact stresses during its service. Usually, these cyclic stresses eventually cause fatigue failure. Accordingly, the fatigue properties are of the utmost importance for the flapper valve material.
A flapper valve made of a steel strip of this invention has its fatigue properties optimized by a combined effect of modifications to the chemical composition of the steel, the non-metallic inclusions and the heat treatment.
Compressor OEMs require materials that have a higher fatigue life to improve the compressor's performance and life.
Furthermore, there is a growing interest in the industry to develop more energy efficient and quieter compressors. The coefficient of performance (COP) can be increased by increasing the valve lift and by reducing the thickness of the valves. Compressor designers therefore require valve materials that have enhanced damping properties in addition to fatigue strength improvement.
The existing steel grades used for reed valves are modified versions of a carbon steel AISI 1095 and a stainless steel AISI 420 produced via conventional melting, casting, rolling and heat treatment processes. However, the industry demands and resulting performance requirements mean that future flapper reeds will increasingly need to be made out of very thin steel strip with an increased fatigue life expectancy and higher damping properties.